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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Identification: Dreissena rostriformis bugensis is a small freshwater bivalve mollusk that exhibits many different morphs; yet, there are several diagnostic features that aid in identification. The quagga mussel has a rounded angle, or carina, between the ventral and dorsal surfaces (May and Marsden 1992). The quagga also has a convex ventral side that can sometimes be distinguished by placing shells on their ventral side; a quagga mussel will topple over, whereas a zebra mussel will not (Claudi and Mackie 1994). Overall, quaggas are rounder in shape and have a small byssal groove on the ventral side near the hinge (Claudi and Mackie 1994). Color patterns vary widely with black, cream, or white bands; a distinct quagga morph has been found that is pale or completely white in Lake Erie (Marsden et al. 1996). They usually have dark concentric rings on the shell and are paler in color near the hinge. If quaggas are viewed from the front or from the ventral side, the valves are clearly asymmetrical (Domm et al. 1993). Considerable phenotypic plasticity of all morphological characteristics is known in dreissenid species and this may be a result of environmental factors, meaning the same genotype may express different phenotypes in response to environmental conditions (Claxton et al. 1998).

Size: Reaching sizes up to 4 cm

Native Range: Dreissena rostriformis bugensis is indigenous to the Dneiper River drainage of Ukraine and Ponto-Caspian Sea. It was discovered in the Bug River in 1890 by Andrusov, who named the species in 1897 (Mills et al. 1996).

Nonindigenous Occurrences:
Canals built in Europe have allowed range expansion of this species, and it now occurs in almost all Dneiper reservoirs in the eastern and southern regions of Ukraine and deltas of the Dnieper River tributaries (Mills et al. 1996).

The quagga mussel was first sighted in the Great Lakes in September 1989, when one was found near Port Colborne, Lake Erie, though the recognition of the quagga type as a distinct species was not until 1991 (Mills et al. 1996). In August 1991, a mussel with a different genotype was found in a random zebra mussel sample from the Erie Canal near Palmyra, New York, and after confirmation that this mussel was not a variety of Dreissena polymorpha, the new species was named "quagga mussel" after the "quagga", an extinct African relative of the zebra (May and Marsden 1992). The quagga mussel has since been found in Lake Michigan, Lake Huron, Lake Erie, Lake Ontario, Lake St. Clair, Saginaw Bay, and throughout the St. Lawrence River north to Quebec City. A 2002 survey of Lake Superior did not detect quagga mussel specimens (Grigorovich et al. 2003), but by 2005 the first quagga mussel was confirmed from Lake Superior in Duluth Superior Harbor (Grigorovich et al. 2008b). A few inland occurrences have been reported in Iowa, Kentucky, Michigan, Minnesota, New York, Ohio, and Pennsylvania. In 2004, very limited numbers of quagga mussels were collected from just two of many sample sites on the Ohio River (Grigorovich et al. 2008a).

The first sighting of quagga mussels outside the Great Lakes basin was made in the Mississippi River between St. Louis, Missouri and Alton, Illinois in 1995 (S.J. Nichols, pers. comm.). In January 2007, populations of quagga mussels were discovered in Lake Mead near Boulder City, Nevada (W. Baldwin, pers. comm.), and in Lake Havasu and Lake Mohave on the California/Arizona border (R. Aikens, pers. comm.). This was an extremely large leap in their range and cause for much concern to limited water supplies and endangered fishes in the southwestern US. In late 2007 and early 2008, quagga mussels were discovered in 15 southern California reservoirs (D. Norton, pers. comm.). Veligers were identified from six Colorado reservoirs (E. Brown, pers. comm.). In Utah, only veligers were collected from Red Fleet Reservoir and just one adult from Sand Hollow Reservoir (L. Dalton, pers. comm.). They are not considered established in Utah. A reservoir in New Mexico tested positive for veliger DNA in 2011.

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Dreissena rostriformis bugensis are found here.

Ecology: They inhabit freshwater rivers, lakes, and reservoirs. In North American populations, they are not known to tolerate salinities greater than 5 ppt (Spidle et al. 1995). Water temperatures of 28°C begin to cause significant mortality, and 32-35°C are considered lethal for Dreissena species (Antonov and Shkorbatov 1990 as cited in Mills 1996). The depth at which the mussels live varies depending on water temperature. They are not generally found in lakes near shore in shallow water due to wave action. The quagga mussel can inhabit both hard and soft substrates, including sand and mud, down to depths of 130 m and possibly deeper. The maximum density of quagga mussels in Lake Michigan is at 31-50 m (T. Nalepa, pers. comm.)

Means of Introduction: The introduction of D. rostriformis bugensis into the Great Lakes appears to be the result of ballast water discharge from transoceanic ships that were carrying veligers, juveniles, or adult mussels. The genus Dreissena is highly polymorphic and prolific with high potential for rapid adaptation attributing to its rapid expansion and colonization (Mills et al. 1996). Still, there are other factors that can aid in the spread of this species across North American waters. Thse factors include larval drift in river systems or fishing and boating activities that allow for overland transport or movement between water basins.

Status: The quagga mussel must have arrived more recently than the zebra based on differences in size classes of initially discovered populations, and therefore it seems plausible that the quagga is still in the process of expanding its nonindigenous range (May and Marsden 1992, MacIsaac 1994). In the 1990s, the absence of quagga mussels from areas where zebra mussels were present may have been related to the timing and location of introduction rather than physiological tolerances (MacIsaac 1994). The quagga mussel is now well established in the lower Great Lakes. This species is found in all of the Great Lakes, but has not been found in great numbers outside of the Great Lakes. This could be due to a preference for deeper, cooler water found in the Great Lakes region as compared to the zebra mussel (Mills et al. 1996). There is a gradient of dreissenid domination in Lake Erie, with quagga mussels dominating eastern basins and zebra mussels dominating the western basin. The same type of gradient was observed in southern Lake Ontario with quagga mussel dominating the west and zebra dominating the east (Mills et al. 1999). If the native habitat of D. rostriformis bugensis is to provide any sort of indicator, the quagga mussel will most likely take over areas where the zebra mussel is now established to become the dominant dreissenid of the Great Lakes (Mills et al. 1996). Indeed, this trend does appear to be occurring in the lower Great Lakes. Mean shell size and biomass increased for both dreissenid species from 1992 and 1995 in southern Lake Ontario (Mills et al. 1999). But the increase was sharper in quagga mussel, and they now dominate in southern Lake Ontario where zebra mussel once did (Mills et al. 1999). At Parker Dam (Lake Havasu) in Arizona, the density was reported at 35,000/sq.m. in 2010 (D. Vigil, pers. comm.).

Impact of Introduction: Quaggas are prodigious water filterers, removing substantial amounts of phytoplankton and suspended particulate from the water. As such, their impacts are similar to those of the zebra mussel. By removing the phytoplankton, quaggas in turn decrease the food source for zooplankton, therefore altering the food web. Impacts associated with the filtration of water include increases in water transparency, decreases in mean chlorophyll a concentrations, and accumulation of pseudofeces (Claxton et al. 1998). Water clarity increases light penetration causing a proliferation of aquatic plants that can change species dominance and alter the entire ecosystem. The pseudofeces that is produced from filtering the water accumulates and creates a foul environment. As the waste particles decompose, oxygen is used up, and the pH becomes very acidic and toxic byproducts are produced. In addition, quagga mussels accumulate organic pollutants within their tissues to levels more than 300,000 times greater than concentrations in the environment and these pollutants are found in their pseudofeces, which can be passed up the food chain, therefore increasing wildlife exposure to organic pollutants (Snyder et al. 1997). Macksasitorn et al. (2015) found that mussel tissue polychlorinated biphenyl (PCB) concentration was positively related to sediment PCB levels, suggesting that quagga (and zebra) mussels might provide an entry point for PCBs into near-shore benthic trophic webs.

Dreissena species ability to rapidly colonize hard surfaces causes serious economic problems. These major biofouling organisms can clog water intake structures, such as pipes and screens, therefore reducing pumping capabilities for power and water treatment plants, costing industries, companies, and communities. Recreation-based industries and activities have also been impacted; docks, breakwalls, buoys, boats, and beaches have all been heavily colonized. Quaggas are able to colonize both hard and soft substrata so their negative impacts on native freshwater mussels, invertebrates, industries and recreation are unclear. Many of the potential impacts of Dreissena are unclear due to the limited time scale of North American colonization. Nonetheless, it is clear that the genus Dreissena is highly polymorphic and has a high potential for rapid adaptation to extreme environmental conditions by the evolution of allelic frequencies and combinations, possibly leading to significant long-term impacts on North American waters (Mills et al. 1996). Dreissena rostriformis bugensis lacks the keeled shape that allows D. polymorpha to attach so tenaciously to hard substrata; though, D. rostriformis bugensis is able to colonize hard and soft substrata (Mills et al. 1996). The ability to colonize different substratas could suggest that D. rostriformis bugensis is not limited to deeper water habitats and that it may inhabit a wider range of water depths where they have been found at depths up to 130 m in the Great Lakes (Mills et al. 1996, Claxton and Mackie 1998).

Remarks: Hybridization between the two introduced dreissenid species is a concern. Zebra x quagga mussel hybrids were created by pooling gametes collected after exposure to serotonin in the laboratory, indicating that interspecies fertilization may be feasible (Mills et al. 1996). Although, there is evidence for species-specific sperm attractants suggesting that interspecific fertilization may be rare in nature, and if hybridization does occur, these hybrids will constitute a very small proportion of the dreissenid community (Mills et al. 1996).

Redear sunfish (Lepomis microlophus) have been shown in experimental enclosers in Sweetwater Reservoir, CA to feed upon and control population sizes of quagga mussels (Wong et al. 2013).

Burks, R.L., N.C. Tuchman, and C.A. Call. 2002. Colonial aggregates: effects of spatial position on zebra mussel responses to vertical gradients in interstitial water quality. Journal of the North American Benthological Society 21(2):64-75.

Claudi, R., and T. Prescott. 2007a. Assessment of the potential impact of quagga mussels on Hoover Dam and recommendations for monitoring and control. Prepared for U.S. Bureau of Reclamation-Lower Colorado Dams Region. Available: http://www.usbr.gov/lc/region/programs/quagga/HooverReport.pdf

Claudi, R., and T. Prescott. 2007b. Assessment of the potential impact of quagga mussels on Davis Dam and Parker Dam and recommendations for monitoring and control. Prepared for U.S. Bureau of Reclamation-Lower Colorado Dams Region. Available: http://www.usbr.gov/lc/region/programs/quagga/ParkerDavisReport.pdf

Claxton, W.T., and G.L. Mackie. 1998. Seasonal and depth variations in gametogenesis and spawning of Dreissena polymorpha and Dreissena bugensis in eastern Lake Erie. Canadian Journal of Zoology 76:2010-2019.

Domm, S., R. W. McCauley, and E. Kott. 1993. Physiological and taxonomic separation of two dreissenid mussels in the Laurentian Great Lakes. Canadian Journal of Fisheries and Aquatic Science 50:2294-2298.

May, B., and J.E. Marsden. 1992. Genetic identification and implications of another invasive species of dreissenid mussel in the Great Lakes. Canadian Journal of Fisheries and Aquatic Science 49:1501-1506.

Mills, E.L., G. Rosenberg, A.P. Spidle, M. Ludyanskiy, Y. Pligin, and B. May. 1996. A review of the biology and ecology of the quagga mussel (Dreissena bugensis), a second species of freshwater dreissenid introduced to North America. American Zoology 36:271-286.

Mills, E.L., J.R. Chrisman, B. Baldwin, R.W. Owens, R. O'Gorman, T. Howell, E.F. Roseman, and M.K. Raths. 1999. Changes in the dressenid community in the Lower Great Lakes with emphasis on Southern Lake Ontario. Journal of Great Lakes Research 25(1):187-197.

Richman, L.A., and K. Somers. 2010. Monitoring metal and persistent organic contaminant trends through time using quagga mussels (Dreissena bugensis) collected from the Niagara River. Journal of Great Lakes Research 36(1):28-36.

Wilson, K.A., E.T. Howell, and D.A. Jackson. 2006. Replacement of zebra mussels by quagga mussels in the Canadian nearshore of Lake Ontario: the importance of substrate, round goby abundance, and upwelling frequency. Journal of Great Lakes Research 32:11-28.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.

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